1. Field of the Invention
This invention is related to the field of storage management and, more particularly, to combining server free and disk-based backup of data in storage networks.
2. Description of the Related Art
The need for data storage capacity in enterprise systems is growing exponentially with no end in sight. One common storage architecture is direct attached storage (DAS). In most DAS configurations, a user's data resides on storage media directly connected to a host/server predominantly using small computer system interconnect (SCSI) technology, and normally there is but a single (i.e. non-fault tolerant) path for retrieving that data. Organizations are beginning to recognize that the restrictions imposed by DAS SCSI architecture are too costly to continue as a viable solution. Such restrictions include the following:                SCSI disk arrays must be located no more than 25 meters from the host server;        The parallel SCSI bus is susceptible to data errors resulting from slight timing discrepancies or improper port termination; and        SCSI array servicing frequently requires downtime for every disk in the array.        
One solution has been to create technology that enables storage arrays to reside directly on the network, where disk accesses may be made directly rather than through the server's SCSI connection. This network-attached storage (NAS) model eliminates SCSI's restrictive cable distance, signal timing, and termination requirements. However, it adds a significant load to the network, which frequently is already starved for bandwidth. Gigabit Ethernet technology only alleviates this bottleneck for the short term, so a more elegant solution is desirable.
Another primary concern of large enterprises is having their data available continuously. In order to insure a high degree of user data availability, data storage should be highly reliable. High reliability data storage is normally implemented by maintaining a backup copy of the data on a physically independent storage device. Under the DAS architecture maintaining a backup copy of user data requires copying the data from storage attached to one host/server to storage attached to another host/server over the LAN used by client/users. As the amount of user data maintained by an enterprise increases, the amount of LAN bandwidth required to perform timely data backup increases proportionately. At some point the copying of backup data may significantly interfere with the client/user's ability to use the network. The storage area network (SAN) architecture may significantly reduce the impact of data backup on the primary network.
The SAN model places storage on its own dedicated network, removing data storage from both the server-to-disk SCSI bus and the main user network. This dedicated network most commonly uses Fibre Channel technology, a versatile, high-speed transport. The SAN includes one or more hosts that provide a point of interface with LAN users, as well as (in the case of large SANs) one or more fabric switches, SAN hubs and other devices to accommodate a large number of storage devices. The hardware (e.g. fabric switches, hubs, bridges, routers, cables, etc.) that connects workstations and servers to storage devices in a SAN is referred to as a “fabric.” The SAN fabric may enable server-to-storage device connectivity through Fibre Channel switching technology to a wide range of servers and storage devices.
Since host primary data is stored on storage devices connected to the SAN, at least some of the SAN storage devices may use disk type technology to provide the access times required by the hosts. Traditionally, the cost of disk type storage has been relatively high and backup of primary data has been to the more mature and cost-effective tape type devices. Using this technology, primary data to be backed up may be read from disk storage by a host/server running a backup application. The host may then write the data to a tape drive storage device. For relatively small amounts of primary data, this method may be sufficient and may not overtax the capabilities of the host or the tape drive.
However, as the amount of data to be backed up increases the difference in speed between tape and disk type storage becomes increasingly significant. Disk type storage devices can be faster than tape by an order of magnitude or more in backup mode and many orders of magnitude faster during restore operations due to its random access capability. Also, as disk drive technology matures, the cost may become competitive with that of tape type storage devices for the backup of primary data making this option financially more attractive.
One way to perform disk-based backup of primary data is analogous to the method described above for tape-base backup. A host/server may read primary data from disk storage and write a backup copy of the primary data to physically separate disk drive devices. Another method for disk-based backup may be referred to as server-free. In a server-free backup environment data is copied directly from a SAN attached storage manager/client disk storing primary data, to a SAN attached backup drive via a SAN data mover using third party copy (3PC) including the SCSI extended copy command. The host/server sends commands to the data mover to tell it which blocks to copy from which SAN attached disk to which other SAN attached device. This method considerably reduces the overhead for primary data backup on the host/server.
Disk-based backup of primary data alone may not be sufficient to meet all the backup requirements of an enterprise. Specifically, data archival and off-site storage for disaster recovery may still require backup using a highly stable, mature technology such as magnetic tape. Also, some large enterprises are reluctant to adopt server-free technology as their method of primary data backup since it does not have an extensively proven track record.